The invention relates to elastomeric bearings which are lubricated by liquids, such as water, and particularly to such bearings which utilize resilient elastomeric bearing portions secured to a rigid, non-metallic, support member.
Liquid-lubricated elastomeric bearings are well-known in the art, particularly in the marine field. Generally, these bearings provide resilient elastomeric bearing portions capable of being lubricated by a particular liquid, such as water. The bearing portions are typically backed by a rigid, non-corrosive, support member. Traditionally, these support members have been of a metal selected principally for its ability to resist corrosion by the liquid with which the bearing comes in contact when in use. In marine use, for example, water-lubricated elastomeric bearing surfaces are typically secured to a bronze, brass, or stainless steel support or backing member.
More recently, there has been increased interest in constructing the support or backing members for such bearings of non-metallic material principally because of the increasing costs involved in the continued use of the non-corrosive type metal supports. In addition, it has been demonstrated that many of the support member metals permit or even enhance undesirable electrolytic action to take place in certain liquid environments, such as sea water. This electrolytic action can detrimentally affect not only the bearing itself, but the structure in which the bearing is being used.
The most popular non-metallic materials currently being proposed for use as a marine bearing backing or support, are structures of thermosetting plastics. These materials are molded or otherwise formed to the shape desired and may include added reinforcement and/or inert fillers. Examples of such proposed structures are disclosed in U.S. Pat. Nos. 3,023,059 and 3,455,619.
By careful selection of particular types of plastic material and/or reinforcement, fillers, etc., a backing or support structure can be made which exhibits adequate structural stiffness and strength to resist the forces to which it may be subjected in use, sufficient resistance to any deleterious effect arising from contact with various liquids, and low water absorption and swell characteristics. Also, these plastic members can be made to maintain sufficient stiffness and strength when heated, a necessary characteristic when using several of the typical methods used in manufacturing elastomeric bearings. In a typical fabrication process, the unvulcanized or "raw" rubber mixture or compound which ultimately forms the bearing portion is molded and cured while disposed against its rigid backing or support structure. Thus, the backing structure employed must not soften or otherwise decompose when subjected to the heat and pressure necessary to vulcanize and mold the bearing portion or portions.
There are, however, certain disadvantages in plastic and/or reinforced plastic structures used for this purpose. The impact strength normally exhibited by these plastic structures is less than satisfactory in many cases. Also, occasional failures of these plastic supports have been observed to be quite catastrophic in nature, thus risking damage to the surrounding structures in which they are housed. Additional cutting and machining of these supports, an operation often necessary in finally finishing the bearings, is sometimes difficult and has caused damage to the cutting and machining tools used.
Also, as in the case of metallic support or backing members, it is usually necessary that these plastic supports be "custom" fabricated in their final configuration in an inventory of various sizes to await final molding and curing of an elastomeric bearing member thereto. This obviously can cause inventory, storage and spatial problems to a manufacturer.